The Amdek Flanger is a useful, high quality effect which can be assembled and modified with the minimum of technical difficulty.

Flanging is undoubtedly a very popular effect with the modern musician producing a distinctive and easily recognisable range of sounds - from a metallic type of phasing to rich chorus effects. It is ideal for treating electric guitars, synthesisers and even vocals. Less expensive drum machines can also be given a welcome boost, enhancing the metallic nature of synthetic cymbal sounds for example.

Amdek's FLK 100 kit can produce a wide range of effects using the four controls: Manual frequency; Modulation Depth and Rate and Resonance or feedback.

The Kit

The Flanger kit is available in bubble-pack form, complete with all parts, a spanner for tightening nuts and detailed instruction sheet. The extra tools required are a 15 to 30W fine tipped soldering iron, wire cutters and strippers, small pliers and a cross-head screwdriver. A 9 volt PP3 battery is needed to power the unit unless you use an external DC 9V power pack.

Parts identification is easily done from the component drawings in the instructions and, once you've laid them out on the work surface, they can be checked off one by one.

Step by step assembly commences with the preparation of 11 lengths of connecting wire for attaching to the four pots - simplified by the provision of a scale and specified lengths for each wire. Useful tips on soldering are also given. In steps 5 to 7 the battery connector, LED and footswitch leads are cut to specified lengths. Then all the necessary soldering to the factory-built PCB (which includes 2 ready-mounted IN/OUT sockets is done (steps 8-9) and the footswitch and LED holder are mounted in the metal case (steps 10 and 11). Soldering the lead wires of the footswitch to the PCB completes the soldering work (step 12).

Now the main components are inserted in the case following steps 13 to 15. The small hexagonal spanner provides easy fastening of the pots and sockets. Care must be taken when inserting the PCB and a plastic insulation sheet provided sticks to the base plate to avoid shorting out the circuit board against the case. A sponge insert holds the battery in place. The base plate screws neatly into place and the rubber battery cover gives simple and effective access without the use of screws (steps 16 to 20). The construction is completed by the addition of two stick-on feet and the four control knobs.

Circuitry

Flanging is produced by adding two signals, one slightly delayed in time with respect to the other, delays normally ranging from 1 to 10mS. The phase cancellations resulting produce a comb filter in the audio spectrum.

Originally this effect was created by recording the signal on two tape decks and slowing one down on playback, by applying friction to the flange of the tape spool - hence the name. Obviously this could not be done in real time and was therefore an effect which could only be produced in the studio.

Analogue delay chains or BBDs (Bucket Brigade Devices) have made it possible to produce this popular effect in real time.

The circuit diagram is shown in Figure 1. Signals from the input are buffered by Q2 then passed through a pre-emphasis circuit, compressor and low pass filter before entering the BBD, IC4, which has 1024 capacitive cells. These are clocked using IC5, a dual phase clock. The clock frequency is varied by the voltage on the Manual pot and the modulation waveform on the Depth pot. Triangle wave modulation is produced by the LFO based around IC3.

A second low pass filter is connected to the output of the BBD to remove any clocking noise. FET switching, Q1, is used to connect the effect.

Original and effect signals are summed at the final de-emphasis op-amp before being connected to the output socket and a bistable flip-flop controls the FET switching from the footswitch.

Operation

The Flanger kit was assembled without any problems and worked first time. If you do have problems, however, you can contact the Roland 'Hot Line' at the UK factory, (Contact Details).

Flanging effects are wide and varied using the four controls to experiment with sounds that are best suited to your playing style.

Modifications

Amdek do not recommend modifications to their circuit 'unless you have powerful tools at your disposal'! However, one modification we made, which does not alter the circuitry, is to connect an external control voltage.

The internal LFO can be disconnected using a switched jack socket and a voltage ranging from 0 to 9V can be used. To fit the socket, drill a hole to suit and connect the centre wiper of the Depth control to the switched side and tag 10 on the PCB to the live side. If no jack is connected, the circuit operates as before. When a jack is connected signals such as those from an external VCO, ADSR, Sequencer, Random Sample and Hold or even Breath Control could be used.

E&MM's special offer price for the Amdek Flanger Kit is £52 inc. VAT and P&P. Please order as: Amdek FLK-100 kit.